1. Field of the Invention
The present invention relates to a recycled paper for electrophotography, mixed with waste paper pulp, and an image forming method making use of the recycled paper for electrophotography. More particularly, it relates to a recycled paper for electrophotography that is preferable for use in electrophotographic apparatus having a photosensitive member cleaning system in which a cleaning member is brought into contact with a photosensitive member to clean the photosensitive member and/or a fixing cleaning system in which a cleaning member is brought into contact with a fixing roller to clean the fixing roller, and an image forming method that forms an image using the recycled paper for electrophotography in an electrophotographic apparatus having such a system or systems.
2. Related Background Art
In recent years, recycled paper is used as paper for electrophotography from the viewpoint of environmental conservation such as saving of natural resources and saving of energy. Such recycled paper comprises deinked waste paper pulp (hereinafter "DIP") made from waste paper comprised of a mixture of a fine class paper and a middle class paper, which waste paper is exemplified by old newspapers, old magazines and waste leaflets commonly released from homes and papers having been used for line printing in computers.
As for copying machines making use of electrophotography, for example, a photosensitive member having photoconductive characteristics is electrostatically charged by means of a primary corona assembly, followed by exposure to light to form an electrostatic latent image on the photosensitive member, and the latent image is converted to a visible image by the use of a toner of a developer according to a one-component or two-component development system to form a toner image. Thereafter, the toner image formed on the photosensitive member is transferred to recording paper separately transported to that portion, by means of a transfer corona assembly, and then the toner image is, as shown in FIG. 9, fixed to recording paper 4 by the action of heat or pressure, or the both, by means of a fixing assembly 13 comprised of a pair of rollers 9 and 10 (or a roller and a belt). A final copied image is thus obtained. In the course of the transfer step, any paper dust generated from the recording paper 4 and the toner having not been transferred to the recording paper are removed at a cleaner zone 1 shown in FIG. 10, provided at the part posterior to the transfer step to carry out cleaning. By means of a cleaning member 2 (e.g., a cleaning blade) brought into contact with a photosensitive member 3, the surface of the photosensitive member is cleaned, and thereafter the step of charging and so forth is repeated. In the fixing assembly (FIG. 9), the toner having not been transferred to the recording paper and the paper dust generated from the recording paper are also cleaned by means of a cleaning member 11 brought into contact with the fixing roller 9, and a release agent such as silicone oil is applied to the roller.
In such a copying machine, recycled paper which is R-paper containing 25 to 30 by weight of middle class waste paper pulp has been used as the recording paper to carry out various tests to obtain the results as shown in Table 1 below.
TABLE 1 ______________________________________ R-paper ______________________________________ Fine class pulp (joshitu kei pulp): 75% by weight Middle class waste paper pulp 25-30% by weight (tyushitu kei koshi pulp): Waste paper pulp content: 70% by weight Scratches/wear on photosensitive X1 member: Scratches/wear on fixing roller: X2 Full-color copied image quality: X3 Brightness: 71.2 Dimensional change due to humidity X4 variations: Occurrence of curl: X5 Runnability: X6 ______________________________________ X1: Visual check on the photosensitive member found conspicuous scratches occurred thereon, which were so serious as to cause faulty images. X2: Visual check on the fixing roller found conspicuous scratches occurre thereon, which were so serious as to cause faulty images. X3: Faulty tint and coloring were seen. X4: Dimensional variations greatly occurred. X5: Curl greatly occurred. X6: Faulty paper transport occurred.
That is, as a result of running tests on a copying machine, the R-paper caused scratches on the photosensitive member, and caused faulty images ascribable to the scratches on the photosensitive member. As for the scratches on the fixing roller, they occurred so seriously as to become visible on the roller after running on about 10,000 sheets, and became so deep as to cause faulty images after running on about 20,000 sheets.
FIG. 8 illustrates how scratches have occurred on the fixing roller. The surface of the fixing roller 9 brought into contact with the cleaning member 11 has been scraped at a zone a because of paper dust having adhered to the cleaning member 11. The paper dust 12 having adhered to the position corresponding to the scratched zone a of the cleaning member 11 has been analyzed to reveal that fibers of middle class waste paper pulp are present. It has been confirmed that this is due to the recycled paper made from middle class waste paper pulp, i.e., the recycled paper made from middle class waste paper such as old newspapers and old magazines.
Similarly, fibers of the middle class waste paper pulp have been also found at the zone where the photosensitive member is scraped.
Also in full-color copied images, the R-paper has caused a poor tint and coloring compared with fine class paper, resulting in a remarkable darkness and tone dullness. This is greatly ascribable to the brightness of the recording paper.
In a further experiment, the amount of a filler in the R-paper was varied to obtain the results as shown in Table 2.
TABLE 2 ______________________________________ Small Large amount amount ______________________________________ Occurrence and directionality of curl: C A-B Lifetime of paper feed roller: Long Short Quantity of paper dust: A C Faulty image due to recording paper: A C Rz (.mu.m): 25.1 17.4 Image density unevenness: C A ______________________________________ (transfer efficiency) A: Good B: A little poor C: Poor (faulty images and paper run)
That is, the larger the amount of the filler is, the less the curl tends to occur and also the curl directionality tends to be improved. What is herein meant by the curl directionality is whether several ten sheets of the same kind of paper having been passed through the fixing assembly have curled in a uniform direction or some of them have curled in various directions. The former is deemed to have a directionality, and the latter, no directionality. In this experiment, paper with a smaller amount of filler shows no directionality.
As shown in Table 2, with an increase in the amount of the filler, the paper dust quantity increases and faulty images due to blank area caused by poor transfer may occur. In particular, it has been confirmed that, with an increase in the amount of a filler of a certain type as in the case of, e.g., calcium carbonate, the lifetime of rollers belonging to a paper feed system becomes shorter because of the wear of paper feed rollers, also resulting in an extremely poor paper runnability.
Namely, the use of a filler in a smaller content brings about an advantage for the recording paper used in electrophotography.
Table 2 also shows the relationship between a surface roughness Rz according to 10-point average roughness of the recording paper and an image density unevenness based on transfer efficiency. With a decrease in the content of the filler, the surface roughness Rz increases and the image density unevenness remarkably occurs. As a result of further detailed studies, the image density unevenness due to a decrease in the transfer efficiency during the transfer step has been found to occur as follows: As shown in FIG. 6 showing a result of simulation analysis, an air gap between paper and a toner layer on the surface of a photosensitive member broadens in accordance with the unevenness of the paper surface, i.e., with an increase in the surface roughness, so that equipotential lines at a convex part (a) and a concave part (b) are formed as shown in FIG. 7, an enlarged view of a region-A in FIG. 6, where the potential at a point i in a given toner layer is lower at the concave part (b) than at the convex part (a). Because of this decrease in potential, the toner layer to be transferred to the recording paper becomes thinner at the concave part (b) than at the convex part (a). In other words, the efficiency of the transfer of toner from the photosensitive member to the recording paper decreases to cause a density unevenness.
In addition to the problems as discussed above, there is a demand for high-quality recycled paper that promises a good runnability of recording paper in copying machines and does not cause any irregularity of sheets in sorters which is due to heat curl.
As also disclosed in Japanese Patent Application Laid-open No. 63-6867, waste paper pulp is commonly mixed in a content of about 70% by weight from the viewpoint of the properties required for recycled paper, i.e., dimensional stability against humidity variations and low heat-curl properties and the viewpoint of making paper runnability stable against an increase in stiffness, and also in view of the suitability as recycled paper for existing electrophotography. From another viewpoint of environmental conservation by less disposal, there is a demand for recycled paper mixed with waste paper pulp in a higher content.
The problems discussed above can be summarized as follows:
1. Some kind of paper dust generated causes a photosensitive member to be-scraped by the cleaning member of a developing assembly, causing a remarkable wear, bringing about faulty images and also resulting in a short lifetime of the photosensitive member.
2. Some kind of paper dust generated causes fixing rollers to be scraped at the cleaning zone of a fixing assembly, causing a remarkable wear, bringing about faulty images and also resulting in a short lifetime of the fixing Pollers.
3. Dimensional variations tend to occur with changes in humidity. PA1 4. The heat generated during fixing has influence on an increase in the occurrence of curl. PA1 5. The stiffness of paper is relatively too low to achieve a stable runnability of copy sheets. PA1 6. Because of faulty running of recording paper, no directionality of the heat curl due to fixing may be ensured to increase the occurrence of curl itself, causing irregularity of sheets in sorters. PA1 7. In the case when a filler is contained in a large amount, paper feed rollers may be remarkably scraped and worn to bring about a faulty runnability of paper in copying machines, also resulting in a short lifetime of the paper feed rollers. PA1 8. The paper dust generated from recording paper increases with an increase in the content of a filler; resulting in an increase in paper dust adhering to each corona assembly, and causing faulty charging such as leakage to give faulty images in some instances. PA1 developing an electrostatic latent image on a photosensitive member through a developing means having a toner; PA1 transferring a toner image formed on the photosensitive member by the development using the toner, to a recording material through a transfer means; and PA1 fixing the toner image transferred to and formed on the recording material, through a fixing means capable of applying the action of heat, pressure or the both of them; PA1 wherein said image forming method has at least one of a photosensitive member cleaning means to clean the photosensitive member by bringing a cleaning member into contact with the photosensitive member after the step of transfer and a fixing member cleaning means to clean the fixing member by bringing a cleaning member into contact with the fixing member; PA1 said recording material comprising a recycled paper comprising a fine class pulp containing a fine class waste paper pulp, wherein said fine class pulp is in a content of not less than 90% by weight based on the weight of the whole pulp, and said recycled paper has a waste paper pulp content of more than 70% by weight based on the weight of the whole pulp.